Such light barriers are known in numerous embodiments. In these, they can be designed in very different sizes and meet very different aims. Thus, for example, the contour of a motor vehicle is scanned inside a car wash system with the aid of appropriately movably arranged light barriers, in order to ensure the vehicle dries as effectively as possible with the least possible outlay on air and energy. It is also known to design very small light barriers in the form of so-called fork light barriers, in the case of which the light path extends between two limbs of a housing. Such light barriers are used, for example, as edge detectors in production machines in which webbed materials are transported in an accurately positioned fashion. If a relatively large limb separation is required for such a fork light barrier, the fork light barrier is replaced by another fork light barrier whose housing has the required limb spacing and in which the supply line to the transmitter in the one limb and to the receiver in the other limb is laid in a suitable way. The use of light barriers of different size at a point of use therefore proves to be troublesome and complicated with reference to handling and stock keeping.